1. Field of the Invention
This invention relates to an image forming apparatus, such as copier, facsimile, and printer, using an electrophotographic process.
2. Description of the Background Art
In an image forming apparatus using an electrophotographic process such as copier, facsimile and printer, the following devices are arranged around a photosensitive body having photoconductivity along a rotating direction of the photosensitive body: a charger, an exposing device, a developing device, a transfer device, a charge removing device, a cleaner, etc. The charger gives a specified potential to the outer surface of the photosensitive body by corona discharge from a charging wire to which a high-tension voltage is applied. The exposing device selectively attenuates the potential of the outer surface of the photosensitive body by projecting a light corresponding to a desired image, thereby forming an electrostatic latent image. The developing device develops the electrostatic latent image formed on the photosensitive body by toner, thereby forming a toner image. The transfer device transfers the toner image formed on the photosensitive body to a transfer sheet. The charge removing device removes electric charges on the outer surface of the photosensitive body. The cleaner removes the toner residual on the outer surface of the photosensitive body.
If a transfer roller is used as the transfer device in such an image forming apparatus, it is normally pressed against the photosensitive body at a specified pressure. The toner image formed on the outer surface of the photosensitive body is transferred to the transfer sheet held between the transfer roller and the photosensitive body by applying a transfer output having a polarity opposite to that of the toner image to the transfer roller.
A known cleaning means for removing external matters such as toner and paper powder adhered to such a transfer roller is such that a cleaning blade formed of an elastic member is held in contact with the transfer roller to scrape off the toner and paper powder adhered to the outer surface of the transfer roller (see Japanese Unexamined Patent Publication No. 8-240998).
In such an image forming apparatus, the transfer roller held in contact with the outer surface of the photosensitive body is required to be made of a soft material in order to increase the lifetime of the photosensitive body by suppressing the abrasion of a photosensitive layer of the photosensitive body. However, if the transfer roller is made of a soft material, the cleaning blade held in contact therewith is also required to be made of a soft material in order not to damage or scratch the outer surface of the transfer roller. In addition, this cleaning blade needs to be held in contact with the transfer roller with a small pressing force.
Accordingly, in order to enable the cleaning blade to be securely held in contact with the transfer roller with a small pressing force, it is required to be highly accurately positioned with respect to the transfer roller. For this purpose, the conventional image forming apparatuses are provided with an adjusting mechanism for finely adjusting the mount position of the cleaning blade. However, such a mechanism results in an increased production cost of the image forming apparatus and necessitates an adjustment of the mount position of the cleaning blade if the cleaning blade is abraded.
Even if such an adjusting mechanism is provided, there are many cases where the toner and paper powder adhered to the outer surface of the transfer roller cannot be sufficiently removed since the cleaning blade is held in contact with the transfer roller with a small pressing force. This may cause the toner to smear the rear surface of the sheet and the remaining external matter such as paper powder to be pressed against the outer surface of the photosensitive body, thereby destroying or damaging it.